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TypeScript ESTree

A parser that converts TypeScript source code into an ESTree-compatible form

About

This parser is somewhat generic and robust, and could be used to power any use-case which requires taking TypeScript source code and producing an ESTree-compatible AST.

In fact, it is already used within these hyper-popular open-source projects to power their TypeScript support:

ESLint, the pluggable linting utility for JavaScript and JSX
Prettier, an opinionated code formatter

Installation

npm install @typescript-eslint/typescript-estree --save-dev

API

parse(code, options)

Parses the given string of code with the options provided and returns an ESTree-compatible AST. The options object has the following properties:

{
  // attach range information to each node
  range: false,

  // attach line/column location information to each node
  loc: false,

  // create a top-level tokens array containing all tokens
  tokens: false,

  // create a top-level comments array containing all comments
  comment: false,

  /*
   * enable parsing JSX. For more details, see https://www.typescriptlang.org/docs/handbook/jsx.html
   *
   * NOTE: this setting does not effect known file types (.js, .jsx, .ts, .tsx, .json) because the
   * typescript compiler has its own internal handling for known file extensions.
   *
   * Exact behaviour:
   * - .js, .jsx, .tsx files are parsed as if this is true
   * - .ts files are parsed as if this is false
   * - unknown extensions (.md, .vue) will respect this setting
   */
  jsx: false,

  /*
   * The JSX AST changed the node type for string literals
   * inside a JSX Element from `Literal` to `JSXText`.
   * When value is `true`, these nodes will be parsed as type `JSXText`.
   * When value is `false`, these nodes will be parsed as type `Literal`.
   */
  useJSXTextNode: false,

  // Cause the parser to error if it encounters an unknown AST node type (useful for testing)
  errorOnUnknownASTType: false,

  /*
   * Allows overriding of function used for logging.
   * When value is `false`, no logging will occur.
   * When value is not provided, `console.log()` will be used.
   */
  loggerFn: undefined,

  /**
   * Allows the user to control whether or not two-way AST node maps are preserved
   * during the AST conversion process.
   *
   * By default: the AST node maps are NOT preserved, unless `project` has been specified,
   * in which case the maps are made available on the returned `parserServices`.
   *
   * NOTE: If `preserveNodeMaps` is explicitly set by the user, it will be respected,
   * regardless of whether or not `project` is in use.
   */
  preserveNodeMaps: undefined
}

Example usage:

const parser = require('@typescript-eslint/typescript-estree');
const code = `const hello: string = 'world';`;
const ast = parser.parse(code, {
  range: true,
  loc: true,
});

version

Exposes the current version of typescript-estree as specified in package.json.

Example usage:

const parser = require('@typescript-eslint/typescript-estree');
const version = parser.version;

AST_NODE_TYPES

Exposes an object that contains the AST node types produced by the parser.

Example usage:

const parser = require('@typescript-eslint/typescript-estree');
const astNodeTypes = parser.AST_NODE_TYPES;

Supported TypeScript Version

We will always endeavor to support the latest stable version of TypeScript.

The version of TypeScript currently supported by this parser is ~3.2.1. This is reflected in the devDependency requirement within the package.json file, and it is what the tests will be run against. We have an open peerDependency requirement in order to allow for experimentation on newer/beta versions of TypeScript.

If you use a non-supported version of TypeScript, the parser will log a warning to the console.

Please ensure that you are using a supported version before submitting any issues/bug reports.

Reporting Issues

Please check the current list of open and known issues and ensure the issue has not been reported before. When creating a new issue provide as much information about your environment as possible. This includes:

TypeScript version
The typescript-estree version

AST Alignment Tests

A couple of years after work on this parser began, the TypeScript Team at Microsoft began officially supporting TypeScript parsing via Babel.

I work closely with the TypeScript Team and we are gradually aliging the AST of this project with the one produced by Babel's parser. To that end, I have created a full test harness to compare the ASTs of the two projects which runs on every PR, please see the code for more details.

Build/Test Commands

npm test - run all tests
npm run unit-tests - run only unit tests
npm run ast-alignment-tests - run only Babylon AST alignment tests

Debugging

If you encounter a bug with the parser that you want to investigate, you can turn on the debug logging via setting the environment variable: DEBUG=typescript-eslint:*. I.e. in this repo you can run: DEBUG=typescript-eslint:* yarn lint.

License

TypeScript ESTree inherits from the the original TypeScript ESLint Parser license, as the majority of the work began there. It is licensed under a permissive BSD 2-clause license.